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DNA: the Molecular Basis of Inheritance

DNA: the Molecular Basis of Inheritance. Chapter 11. DNA: the genetic material. In the 1860’s Mendel verified that traits were inheritable components passed from parent to offspring. These traits seemed to obey certain laws. What were the laws that inheritable traits obeyed?.

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DNA: the Molecular Basis of Inheritance

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  1. DNA: the Molecular Basis of Inheritance Chapter 11

  2. DNA: the genetic material • In the 1860’s Mendel verified that traits were inheritable components passed from parent to offspring. • These traits seemed to obey certain laws. What were the laws that inheritable traits obeyed?

  3. DNA: the genetic material • By the 1920’s it had been established that chromosomes were the basis of inheritance. Scientists understood it was something in chromosomes that caused the multitudinous variety of organism present on earth. What are the two components of chromosomes? What is the structure of chromosomes?

  4. The structure of chromosomes:

  5. The Griffith Experiment: • Showed that DNA was the material that transferred inheritable traits • Was a “lucky” find • Griffith’s experiment with Streptococcus pneumoniae • His experiment was confirmed by Oswald Avery in 1944 • What was the significance of these two experiments?

  6. DNA or Protein? • Why would protein be a good candidate for passing on of hereditary material? • Why was DNA not thought to be a good candidate? • How was DNA shown to be the real “power” behind inheritance once and for all? • Hershey and Chase experiment

  7. Hershey-Chase experiment:

  8. Watson and Crick and Chargaff and Franklin and Wilkins and… • Using the information gathered by Erwin Chargaff, Maurice Wilkins and Rosalind Franklin, Francis Crick and James Watson were able to deduce the structure of DNA: a double helix surrounding paired nitrogen bases • Back ground and explanation of DNA structure

  9. The nature of DNA replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” - J.D. Watson & F.H.C. Crick in “Molecular Structure of Nucleic Acids: A Structure for Deoxynucleic acids”

  10. How does DNA replicate? • The two DNA strands by being complementary to one another serve as a template for new strands (semiconservative model) • Other models of replication had to be rejected (conservative, and dispersive) • Meselson and Stahl’s experiment

  11. The enzymes of replication • Helicase • Primase • DNA polymerase I • DNA polynerase III • DNA ligase • Single strand binding protein • DNA topoisomerase • Telomerase

  12. Telomeres • Repetitive strands at the end of chromosomes • Human sequence is TTAGGG repeated about 2500 times • Per replication each human loses about 50-200 base pairs • Cells die after about 20-30 divisions • Telomerase regenerates telomeres

  13. DNA proof reading and repair • 1 base pair in 106 is mismatched • Result would be 1000 mutations per cell division • Mechanisms are in place to proofread and repair DNA

  14. DNA proofreading • DNA polymerase “reads” DNA strand and finds mismatched bases. • The mismatched base is excised and replaced • Lowers the error rate to one in 1010 • How does the DNA polymerase “know” which strand is faulty?

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